Reflective roofing has long seemed one of the best geoengineering options to help turn the rising tides of Global Warming. An opportunity to reduce energy use through reduced cooling demand and longer lasting roofs, to improve urban life (and cut energy requirements) by reducing urban heat island impacts, and to contribute to fighting global warming by reflecting solar radiation back into space.
It seems, however, that this opportunity might be even greater than previously believed. 
Global Cooling: Increasing World-wide Urban Albedos to Offset CO2 (pdf) suggests that white roofing of just 100 cities could halt Global Warming temperature increases for a decade or more.
This study comes from some of the nation's top expert groups in roofing, from the Heat Island Group at Lawrence Berkeley National Laboratory which focuses on this serious urban challenge:
"Heat Island research is conducted to find, analyze, and implement solutions to the summer warming trends occurring in urban areas, the so-called 'heat island' effect. We currently concentrate on the study and development of more reflective surfaces for roadways and buildings."
Take a moment to conceptualize this in your own way.
Mine: consider walking barefoot onto a road on a hot, sunny, summer day. Ouch! Doing a ballet of quick steps, trying to keep from broiling the feet, sweet relief when on a painted white line or getting to a white concrete curb. Even when not actually on the blacktop, think about standing by the side of the road, feeling the wave of heat rising from the blacktop. It is not hard to visualize the heat collected by low albedo (that means low reflective) surfaces.
Another image: School buses increasing have white roofs. Why? To reduce the heat load within. 
This saves fuel (air conditioning) and reduces the sweat load for kids within. Energy (financial) savings and improved comfort. A win-win space.
And, just as moving from blacktop to white line or asphalt to concrete provides a comforting drop in temperature, so too can changing roofs / surfaces create a real change in the amount of solar radiation captured by man-made structures.
a 1,000-square-foot roof -- the average size on an American home -- offsets 10 metric tons of planet-heating carbon dioxide emissions in the atmosphere if dark-colored shingles or coatings are replaced with white material.
Consider that. Per 100 square feet moving from traditional heat-absorbing shingles to reflective, high-albedo roofing is an offset of a ton of CO2 emissions.
Globally, roofs account for 25% ofthe surface of most cities, and pavement accounts for about 35%. If all were switched to reflective material in 100 major urban areas, it would offset 44 metric gigatons of greenhouse gases, which have been trapping heat in the atmosphere and altering the climate on a potentially dangerous scale.
That is more than all the countries on Earth emit in a single year. And, with global climate negotiators focused on limiting a rapid increase in emissions, installing cool roofs and pavements would offset more than 10 years of emissions growth, even without slashing industrial pollution.
To be clear, simply addressing temperature 
will not deal with all of the challenges related to CO2 emissions. For example, reflective roofing would do nothing relative to the acidification of the oceans and this threat to ocean (and human) life. But, the temperature impact in terms of cooling could be quite important in helping to create breathing space as humanity lowers its carbon footprint through reduced energy use combined with ever-more low/no-carbon energy sources.
The core geoengineering principle should be:
win-win-win. A proposal that, in a systems of systems effort, provides multiple wins and does not solely address temperature. Thus, a proposal that offers real potential for improving economy, reducing carbon, and contributing to reduced temperature (both directly, somehow, and indirectly through reduced carbon loads or carbon capture) would seem to merit greater prioritization than high-cost efforts that would solely impact "temperature" but not impact (or worsen) the carbon load equation.
And, reflective roofing certainly is in this space. Reflective roofs reduce energy costs, with the 'payback' period for the additional cost of a reflective roof over traditional asphalt sometimes as short as a few weeks due to significantly reduce air conditioning loads. As well, if the air conditioning is on (or near) the roof (as many are), this will further save energy by making these systems that much more efficient. In addition, there is reduced maintenance costs as reflective roofing requires less maintenance as they have lower temperature extremes and swings during the year, thus lasting longer..
A reasonable place to start for more information the Energy Star page on reflective roofing.
Americans spend about $40 billion annually to air condition buildings -- one-sixth of all electricity generated in this country. Why choose ENERGY STAR reflective roofing for your building?* ENERGY STAR qualified roof products reflect more of the sun's rays. This can lower roof surface temperature by up to 100F, decreasing the amount of heat transferred into a building.
* ENERGY STAR qualified roof products can help reduce the amount of air conditioning needed in buildings, and can reduce peak cooling demand by 10-15 percent.
And, of course, this moves beyond the savings on the specific building when we look to reflective roofing on a large scale,
"I call it win-win-win," Akbari said. "First, a cooler environment not only saves energy but improves comfort. Second, cooling a city by a few degrees dramatically reduces smog. And the third win is offsetting global warming."
Some questions to consider
Here is an Energy Smart change that could have a major impact ... quickly. It is time to Get Energy Smart! NOW!!! And, on our rooftops might be a good place to start.
NOTES:
1. Since diving into the deep end when it comes to energy issues, almost every day sees new fascinating concepts, approaches, and technologies. Fascinating ... exciting ... even hope inspiring at times. And, as well, as the passion builds, so many of these are truly Energy COOL.
2. Hat tip to Grist , EcoGeek, and Treehugger. LLBL press release.
Follow A. Siegel on Twitter: www.twitter.com/A_Siegel
I'm also interested in the energy capture of heat escaping from buildings (and roads?) and how this energy could be used in overlapping ways. It may be in small ways that it can be utilized but it could utilized in creative ways -- such as outdoor light generation and other low-watt purposes.
In the colder latitudes, heat loss during the winter months may somewhat offset savings in the summer months.
To be clear, simply addressing temperature will not deal with all of the challenges related to CO2 emissions. For example, reflective roofing would do nothing relative to the acidification of the oceans and this threat to ocean (and human) life. But, the temperature impact in terms of cooling could be quite important in helping to create breathing space as humanity lowers its carbon footprint through reduced energy use combined with ever-more low/no-carbon energy sources.
This could help create breathing space for other actions to have impact to reduce, and then reverse, CO2/other GHG buildup.
WHAT helps is that we have about 3 feet under the house and just turn on the air fan when we need it and it brings in cool air. We also have an under the house heating system. Now that really isn't much but since it blows heat out from floor level (you know the kind, on cold mornings you stand over it and it blows warm air up your bathrobe?) which we've found warms the house faster than one blowing warm air from above. Since heat rises, it takes more energy to warm the room.
NOW if we could just afford solar panels, we'd have it made energy wise.
Would love to put in a water cistern. With the rain we get we could easily save up to several thousand gallons of water.
OH well every little bit helps.
Electric cars are the best future.
Note that man's "black", low albedo roofs are part of the problem ... this helps reduce that portion of the problem set.
FYI -- Totally frustrated as well.
We need to be going strong and fast on all fronts: energy efficiency, changing lifestyle patterns (from cloth bags, to eating locally, to smart growth, to ...), to renewable energy to remediation (forest protection, reforestration, better agricultural practices, ...). We need to be putting in place things that work today (like reflective roofing ...) while investing to develop new technologies, better practices, new concepts, etc ...
2. Remember that most of America isn't at California building standards re energy efficiency. (Though, if we went that route ...) And, that much of this is appropriate for retrofit with roof repairs/such.
3. re turning temperature up ... the reality is, why not both? White roof requires heat load (efficiency), changing thermostat is lifestyle choice (conservation).
I whipped up a basic 25,000 square-foot two-story office building in Los Angeles that meets the latest Title 24 code requirements for new construction in California. This is not a crappy building; it is well-insulated with a modest amount of high-performance windows and an industry-leading packaged rooftop air-conditioning system.
I ran an annual simulation once with a roofing solar absorbance of 0.7, corresponding to a typical dark roof, and again with the absorbance at 0.3, corresponding to a Cool Roof Rating Council (CRRC) certified roofing surface. No other modifications were made.
The cool roof produced modest but measurable savings: 1% lower carbon footprint, 2% less annual air-conditioning electric consumption, and 3% less air-conditioning electric demand under peak conditions.
The savings would certainly be more substantial for retrofitting an existing building that doesn't come close to meeting today's stringent efficiency standards. But even for a modern green building, it's a very cost-effective energy conservation measure in the majority of U.S. climate zones.
Cool roofs don't have to be white, either. A wide variety of colors can be used. There's even commercial additives that can increase the solar reflectance and thermal emittance of most exterior paints.
As I understand it, the model is building specific and does not deal with heat-island impacts / benefits.
In addition, wonder what percentage of flat-roofed commercial buildings have air conditioning systems on the roof, being heating by the roof?
Most flat-roofed commercial buildings have rooftop packaged DX units, and the ones that don't generally have rooftop chilled water air-handling units. The cabinets of these units are typically made of highly reflective metal, and most are fairly well insulated. It's standard practice to disregard heat gain through the AHU, but it does exist.
My firm almost exclusively takes high-end clients that are committed to exceptional efficiency and expect U.S. Green Building Council's LEED Gold or Platinum certifications. So our designs tend to be a little exotic. We've almost single-handedly introduced active chilled beams to America, and many of our designs achieve their cooling effect purely through the evaporation of water instead of through compressor-based refrigeration units. These technique work especially well in the same climates where cool roofs excel: mild-to-hot and relatively dry.
One of those is to change our energy systems over to renewables, first and foremost solar energy. I would estimate that the total cost of painting the roofs in 100 cities world wide is orders of magnitude higher than our current annual investment in solar energy.
Developing solar energy is basically only limited by financial constraints. If the choice were to invest the money in painting roofs white (which will cost thousands of dollars per roof in developed countries) and doubling our solar panel production in 18 months rather than 24 (or so) for the next ten years, I would opt for the latter. And probably so would the LBNL group. If they had a real choice, that is. In reality we will simply do neither.
And, that reduced energy use has direct implications for reducing carbon footprints of (especially) commercial structures that get white roofed.
And, the payback in terms of cost per kwh is far better from the energy efficiency due to white roofing than what would occur with any active renewable energy option.
Don't disagree that I would love to see massive deployment of energy efficiency and renewables ... but, white roofing is part of energy efficiency and should not be talked about as some form of enemy of renewables.
Solar panels lower the heat flow through the roof structure just like white paint does. A panel that is 15% efficient will immediately convert 15% of the incident radiation into electricity and that electricity will generate heat somewhere else, but not on the roof. The remaining heat will heat the panel, which is cooled by the surrounding air (either by the wind or the self generated convection if proper distance from the roof is maintained), not the roof. Which lowers the cooling demand just the same way as the white paint does.
Having said that, white paint will not significantly reduce the heating necessary in winter. Which leads to the conclusion that we should have insulated our roof well to begin with because in terms of bang (lbs. CO2) per buck that is the single best investment we can make. Which, incidentally will already lead to a significant reduction of our cooling cost...
On top of that most of the summer heat gets into small buildings through the windows, not the roof.
I think if this is an attempt to answer the question what Scrooge McDuck would do to combat global warming, then we might have a winner.
In the real world, however, well insulated black roofs that generate electricity are the one and only correct solution.
Step 2: Increase efficiency
Step 3: Add renewables
Otherwise -- and I apologize in advance -- we're just putting lipstick on a pig.
Cool roofing, like adding exterior or duct insulation, installing CFL or LED lighting, upgrading windows or installing exterior shading devices, etc. falls under step 1. Switching from reciprocating to scroll DX units, furnaces to condensing boilers, air-cooled to water-cooled condensers (including ground-source water loops), etc. fall under step 2.
It doesn't make all that much sense to go straight to step 3 with photovoltaics if you haven't considered the various options under steps 1 and 2. You'd just be spending too much money on an oversized PV array. Watch for government agencies increasing their prescriptive efficiency standards for commercial and residential building owners seeking public funds for PV retrofits, because they've already cracked down on new construction.
First link is to a 'geoenginnering' discussion of mine from awhile ago in which reflective roofing is discussed, for example ... and I don't want to claim any 'first thinker' rights to this.
Wilbur